First things first.
Are you running Mods? If so are they game killers if you're not using them. Remove from mod list or modify load sequence. Are non steam workshop mods fully up to date?
If you installed from steam. Revalidate your files.
Go back a few saves to when it didnt happen, maybe from a day or two ago, Its possible a save was corrupted and has input corrupted data into subsequent saves.
Update your system. All of it, including Windoze. Windows security often stops legitimate things running if your system isnt fully up to date but your other programs are. I.e my soundcard fails every time it updates and windows hasnt yet.
What system are you running, how much RAM headroom do you have.